A voyage into the mysterious world of alien intelligence Do advanced life forms exist beyond Earth? Is there intelligent life elsewhere in the cosmos? Ask an astrobiologist, and you will usually get back a qualified "yes." But further investigation of the question is stymied by our reliance on concepts that remain elusive. What do we mean by "advanced" or "intelligent"? Faced with this problem, most astrobiologists turn their attention to more tractable scientific issues, examining geological and biological conditions for life on Earth to propose how it might have arisen elsewhere. Their aim is to understand life, of whatever sort and wherever it occurs, as part of processes of planetary formation and change. Gary Tomlinson extends this scientific method as only a humanist can. Starting from a reconsideration of the nature of meaning-making on Earth, he opens a new path toward the perennially alluring question of alien intelligence. Evolutionary science, information theory, and the constraints under which signs occur-or semiosis-join in his account to delimit the grounds for the emergence of meaning-making life forms anywhere in the cosmos. Tomlinson identifies conditions that must pertain wherever signs arise, describes ways signs gather into systems, and shows how such systems underlie culture and technology. Working from the earthly example, he discerns kinds of evolved features plausibly required for organisms to meet these conditions, and he gauges the likelihood of this meeting in extraterrestrial biospheres. Astrosemiosis offers a picture of sign making as a planetary process, narrowing the gap between speculative thought on smart aliens and empirical astrobiological science.